1. Field of the Invention
The present invention relates to a storage apparatus which records and reproduces data on or from a magnetic disk medium by the perpendicular magnetic recording process and a control method thereof, particularly, to a storage apparatus which monitors a signal frequency band of write data at a head IC and detects an abnormality and a control method thereof.
2. Description of the Related Art
A conventional magnetic disk apparatus is based on the longitudinal magnetic recording process, in which a signal is recorded by magnetizing a magnetic layer in a direction in parallel with the surface of a magnetic disk medium. This results in magnetic poles facing each other at bit boundaries at a high recording density, thus leading to instability.
For the purpose of solving this problem, a magnetic disk apparatus based on the perpendicular magnetic recording process has recently been industrialized. The perpendicular magnetic recording process is to record signals by magnetizing a magnetic layer in a direction perpendicular to the surface of a magnetic disk medium. It brings about stabilization at high densities since magnetic poles attracting each other face each other at bit boundaries, and permits high-density recording of over 100 giga bits/in2.
In perpendicular magnetic recording, however, presence of a wide DC signal recording area in the magnetic disk medium, if any, causes occurrence of a strong leaking magnetic field on the medium. When reading out a magnetic disk medium having data recorded by the perpendicular magnetic recording process via a read head element such as a GMR element, the symmetric amplitude converting property of the read signal relative to the recording magnetic field becomes asymmetric under the effect of the leaking magnetic flux. This may cause degradation of the read signal and worsening of the error rate.
In a magnetic disk apparatus based on perpendicular magnetic recording, therefore, write data entered into a write amplifier of the head IC through run length conversion fall within a sufficiently high write data signal band so as not to contain a low-frequency signal component which may cause worsening of the error rate. As a result, even when perpendicular recording is made onto a magnetic disk medium, the DC signal recording area does not spread.
In such a conventional magnetic disk apparatus based on the perpendicular magnetic recording process, however, write data entered into the write amplifier of the head IC by the signal method of the read channel is converted so as not to contain a low-frequency signal component. The head IC, mounted on an arm of the head actuator driven by the voice coil motor, is wired with a flexible printed circuit (FPC) with the read channel on the circuit board. Since it is always deformed by the action of the arm, the line impedance varies, depending upon the state of deformation, leading to dull signal waveform, and this may cause an increase in low-frequency signal component of the write data.
The increase in low-frequency component caused by the signal waveform becoming dull of the write data causes an increase in the DC signal recording area of the magnetic disk medium, resulting in an increase of leaking magnetic fluxes. As a result, the symmetric amplitude conversion property of the read signal relative to the recording magnetic field becomes asymmetric under the effect of the leaking magnetic fluxes, and a problem intrinsic to perpendicular magnetic recording is encountered here in that deterioration of the read signal leads to worsening of the error rate.